Method of treating roadways



Patented July 241, i923 SAM EVERETT FINLEY,

OF ATLANTA, GEORGIA.

METHOD OF TREATING ROADWAYS.

No Drawing.

To all whom it may concern.

Be it known that I, SAM E, FINLEY, a citizen of the United States, resident of the city of Atlanta, county of Fulton, State of v Georgia, have invented certain new and useful Improvements in Methods of Treating toadways; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

The invention relates to the construction of permanent roadways which include a wearing surface of broken stone, gravel, slag, or other mineral aggregate, laid upon a foundation of concrete, broken stone, sand, clay, top soil, gravel, water bound macadain, or similar material which constitutes a flexible or semi-flexible base, and has for its 0bject to provide a more thorough impregnation or penetration and a better incorporation of a bituminous binding agent with the mineral aggregate wearing surface, also, to effect an eflicient union or bond between the mineral aggregate wearing course and the foundation. To this end the invention involves the wetting of the mineral aggregate -wearing surface, after the latter has been applied to the foundation and worked to proper grade, with a suitable fluid, preferably water, which is supplied in sufficient quantities to free the aggregate of loose dust, clay, or other foreign material, to effectively wet the cleaned surfaces of the aggregate, and to impregnate the upper surface of the foundation to a sufiicient extent to cause the angular fractures of the aggregate to be imbedded in the surface of the foundation and thereby key the aggregate of the wearing surface securely to the foundation, the

wetted aggregate of the wearing surface be-.

ing then coated with a bituminous binding medium which, because of the presence of the wetting agent, eventually effects a closer and more intimate union or incorporation with the material of the wearing surface, so that a highly efiicient, durable, waterproof, wear resisting road surface results, due to the bituminous binder working into the pores or interstices of the individual elements of the mineral aggregate, and also penetrating to practically the full depth of the wearing metal, so that the entire body of Application filed November 7, 1919. Serial No. 336,453. 1

the latter isefi'ectively bound together by the cementitious qualities of the bituminous material. It has been the general practice heretofore in constructing roadways, involving a Wearing surface of broken stone, or other mineralaggregate incorporated with a bituminous binder, to stipulate as one of the conditions precedent to the application of the binder, that the material of the road wearing surface, consisting of broken stone, gravel, slag, or the like, be free from moisture. Indeed, so' vital has this requirement been regarded that, in cases wherein it was found expedient to sprinkle a road surface with water to lay and partially wash off the dust preparatory to making a'surface application of oil, tar, or the like to the road, it has been the universal custom to allow suflicient time for the water to completely evaporate before attempting to apply the oil or tar, or other surface treating medium. In fact, the presence of water or a wetting medium, involving water, in any appreciable amounts in the relatively loose. and porous material of the wearing surface of a road, was generally regarded asobjectionable and deleterious to the practical and eflicient incorporation of bituminous and similar heavy binding media by the so called penetration method, in which the binder passes into the interstices-be tween the elements of the wearing surface for the purpose of cementing the same into a strong resistant body, capable of withstanding the effects of heavy trafiic.

After extended experimentation, both in practical road construction and in extensive laboratory tests, I have found that moisture, when applied in sufiicient quantities to wash the mineral aggregate free of loose adher ing foreign materials and also to penetrate the foundation of the roadway for a distance from one-half inch to one inch, in-

stead of proving a detriment to the subsequent treatment of a road surface with a bituminous binder by the penetration method, proved to be'a decided advantage or asset, inasmuch as it permitted the use of bituminous binders of high stability and,

.theref ore, greater cementing values, securing a more effective and cleaner incorporation between the road metal proper and the binder, as Well as obtaining a complete union between the wearing, surface and the foundation, all of which advantages could not have been foreseen or predicated upon the known practice of treating roadways with admixtures of water and chemicals, or

V with emulsions of water and relatively light there will always be a portion of such material coated with a thin layer of fine dust, clay, sand, or other finely divided foreign matter which, if allowed to remain, actsas a separator between the bituminous binder and the wearing metal proper, provided the binding material has the necessary stability or cementing value, so that the bindingnredium, which must be heated to a relatively high temperature in order to reduce it to the necessary condition of fluidity for successful application, after giving up its heat, cannot effect a satisfactory union with the mineral aggregate of the wearing surface and the latter tends 'to work loose and ravel out of the road surface. For similar reasons, no union can be obtained between the foundation and the wearing course metal. when such foundation depends upon moisture as a binder, such as would be the case when sand, clay, or water bound macadam foundations are employed, as the same separation between the foundation and the wearing course would prevail, because of the fine dust and foreign material which lies on the surface of the foundation prior to the placing of the wearing course metal thereon. These objectionable conditions are completely obviated by the novel mode of treatment constituting the present invention.

In the practice of the invention, after the wearing course, constituted as hereinbefore indicated, has been distributed over the foundation to the desired thickness and cross section, water or other suitable liquid is applied by any appropriate apparatus, in such quantity per surface square yard of road, as will wash from the road metal all dust, or loose finely divide-d matter and carry the same to and into the surface of the foundation, the liquid effectively wetting and penetrating to some extent the surfaces of the road metal and also penetrating the foundation to the extent of from one-half inch to one inch in depth so as to soften the surface of the foundation. Preferably, the wetted road metal is treated with a heavy road roller or other suitable apparatus which has the effect of compacting the road metal to the extent of forcing the angular fractures of the lower courses of the metal into the softened surface of the foundation and causing the plastic metal of the latter to be forced up beneeaeoa tween the various elements of the road metal,

so that, when the moisture has'been ultimately dissipated by evaporation, or absorption, the union between the inaterial of the wearing surface and the foundation is complete and efiicient, and after the wearing surface has been treated with the bituminous binder, the wearing coating is securely locked to the foundation.

Before the moisture applied to the material of the wearing surface material has had time to evaporate, to any material extent, and while the moisture is still adherent to the superficial surfaces of the road metal and penetrates the pores of the latter to an appreciable degree, the bituminous binding material is applied to the road in appropriate quantities and by any suitable form of apparatus, preferably and more conveniently by means of one of the spraying machines adapted to spray the highly heated bituminous material onto the road surface in theform of a uniform sheet or layer, the bltll? minous material working its way down into the interstices between the road metal and ultimately binding and cementing the latter together as a homogenous mass to; the full depth of the complete layer of wearing material. Ordinarily, it has'been found difficult to effect a deep penetration into the road metal by the heavy bituminous binders, but it has been found that, according to the present method, the water which coats the road metal, increases the penetration qualities of the bituminous binder, as the latter has been found to spread more thoroughly and effectively over a wetted stone surface than it would over the same surface in an absolutely dry condition. It has also been found that the bituminous binder effects a firmer union with the individualelements of the wearing material of the road surface, when the latter are coated with water, and this effect is apparently due to the following conditions, which a series of laboratory tests have indicated: First. The washing of the stone or mineral aggregate with water removes from its surface such dust and loose particles as would interfere with the close contact with the binding medium.

Second. None of the stone is saturated with water, therefore, the capillary action between the water and the porous surfaces of the stone carries the surface film of water into the stone, compressing the air within the capillary tubes and creating apartial vacuum at the outer ends of said tubes, the unbalanced pressure thus caused forcing the bituminouscoating into, the pores of the stone.

Third, The contact of the relatively hot bituminous binding material with the film of water covering the surfaces of the road metal serves to vaporize a portion of the water, and the steam thus formed subsequently condensing in the bituminous coating partially emulsifi es the bituminous ma terial and, therefore, increases the fluidity of the mixture and causes it to more readily penetrate the pores of the road material by capillary action.

Fourth. The subsequent loss of this entrained water by evaporation, reduces the consistency of the bituminous coat to its original quality orcharacter, so that each individual element of the road metal is effectively coated with a closely adherent body of bituminous binder, which also penetrates the pores of the solid road material. The bituminous binder, therefore. when reduced to its ultimate condition by loss of its applied heat and the ultimate evaporation of the water entrapped thereby, serves to bind the wearing material of the road surface together in a most intimate union, which extends throughout the depth of the wearingsurface, the adhesion of the binding medium to the road metal, and the penetration of the binder into the road surface being materially enhanced by the use and presence of the moisture as applied to the road material.

It has been effectively proven that roads constructed in accordance with the present invention are much more durable than similar roads constructed with the same mate rial but without the use of water or a similar wetting agent preparatory to the application of the binding medium. the principal reasons for the increase and efficiency being thegreater and more effective penetration of the binding medium into the surface wearing coat of road metal, and the greater adhesion between the binding medium and the road metal, produced by the effect of the water or wetting agent, as hereinbefore described.

A still further advantage of the use of water occurs in cases wherein the foundation of the road is constructed of material involving water as its binding agent, for instance. such as sand, clay, gravehtop soil, water bound macadam, or the like, for the reason that if any portion of the foundation had not received sufficient moisture in the first instance to produce a coherent surface structure,'and would, theref ore, tend to work or scour out after the road had received its wearing coat of mineral aggregate or the like, the application of the water in carry-- ing out the present method would correct the deficiency in the impaired portions of the foundation and leave the latter in proper form for effective union with the road metal when the latter is rolled onto the foun dation. i

It will be apparent that under certain conditions the mineral aggregate may contain closely adherent clay or similar material, which cannot be Washed off by the wetting medium, but this fact will -not,materially affect the successful operation of the method inasmuch as the Wetting medium \villpenetrate the adherent clay or foreign material and render the same capable of absorbing the'-' bituminous binder,- whichultimately reaches the faces of the mineral aggregate and effects the desired union between the individual elements of the aggregate.

It is also to be noted that any loose dust or foreign material which is washed from the mineral aggregate is carried into the surface of the foundation where it becomes valuable as a binding medium between the foundation and the wearing course, after the water has been applied, and in case the foundation is in itself'constituted of a water bound medium, the dust or other foreign material washed down onto the foundation \vill supplement the effective binding action between the foundation and the wearing course.

Another highly important and valuable result which follows the wetting of the mineral aggregate, preparatory to applying the binding medium,is the fact that the wetting medium covers all of the superficial surfaces of the mineral aggregate, including the lower or bottom surfaces, which would not ordinarily be reached by an applied oil or other binding medium, but which when once Wet with water or aqueous solution, are covered on all sides by the fluid asphalt or other binding medium, so that not only thetop and side. surfaces of the mineral aggregate are covered, but also the bottom surfaces are completely coated and the union or admixture of the mineral aggregate with the binder is practically as effective as it would be if the materials were mixed before they were applied to the road surface. This is a novel result which, so far as applicant is advised, has never been obtained by any of the previously known methods of applying heavy binding media. to road surfaces and has the effectof drawing the binding medium into all of the voids between the elements of the mineral aggregate, whereby a complete homogeneous union between the aggregate and the bindin medium is obtained.

It is to be understoo. that no specific limitations as to the time interval between the application of the wetting material to the mineral aggregate and the application of the binding medium thereto can be. laid down, but sufficient time should be permitted to elapse, after the application of the wet ting medium, to allow the latter to penetrate the road metal, 'wet all the surfaces thereof, be absorbed to some extent by the porous road metal, and topenetrate the surface of the foundation to a sufficient extent to soften the latter so that the subsequent rolling operation will force the vroad metal into the softened surface of the foundation and effect the necessary union between the foundation and the Wearing course. It will be understood, therefore, that the time interval between the application of the wetting medium and the binder must be regulated by the conditions met by the road engineer, not only in respect of the particular character of the road and its wearing course, but also the climatic and weather conditions. It has been found that the best results follow when the wetting operation has been applied sufliciently in advance of the application of the binding medium, to thoroughly coat and partially impregnate all of the surfaces of the road metal or mineral aggregate, so that the binding medium subsequently applied will follow the moisture and similarly coat and impregnate all of the faces of the road metal.

It has also been found to'be of advantage, in certain cases, to make a second application of the wetting medium to the road surface, after the latter has received the application of the binding medium, and preferably just before the road surface is rolled. This second application of the wetting medium, under certain conditions, produces a much more effective penetration of the binding medium and carries the same to all parts of the-road metal and through the layer of the latter to the surfaceof the road founda tion, thereby producing not only a better union among the various elements of the wearing course, but also more effectively keying the latter to the foundation during the rolling process.

While it is recognized that it is not novel, in a broad sense, to apply water to a road surface either prior to or coincident/with the application of a light oil, for the pur- "pose of laying the dust or improving the surface of a road, nevertheless, so far as applicant is aware, he is the first to employ and app-1y a wetting agent to the relatively loose mineral aggregate or wearing course of a road to effect the highlv beneficial and improved results set forth and involving the use ofhighly stable binding media which v are caused to penetrate substantially the entire body of the wearing coat.

' What I claim is:

1. The method of constructing road surbroken stone or other mineral aggregate to the foundation, wetting the aggregate sufficiently to wash adhering loose foreign matter therefrom and coat and partially impregnate the aggregate with the wetting medium, and covering the wetted aggregate with a penetration coating of heated bituminous binding medium; whereby a better penetration and incorporation of the binder with the aggregate isef'fected.

2. The method of constructing road surfaces which comprises applying a layer of broken stone or other mineral aggregate to the foundation, wetting the aggregate with sufficient water to free the aggregate of dust and other loose foreign material and partially impregnate the elements of the aggregate, and before the water evaporates ap-v plying a penetration coating of heated bituminous binding material of high'stability to the aggregate; whereby a better penetration and incorporation of the binder and the aggregate is effected.

3. The method of constructing road surfaces which comprises applying alayer of broken stone or other mineral aggregate to the foundation, wetting the aggregate with s'ufiic-ie-nt water to free the aggregate ofdust and other loose foreign material to partially impregnate the elements of the aggregate and to penetrate the foundation, rolling the wetted aggregate to force the lower portions thereof into the foundation, andcove-ring the wetted aggregate with a penetration coating of heated bituminous-binding m-ateri-al of high stability; whereby an effective union between the foundation and the aggregate is producedv and a better penetration and incorporation of the binder with the aggregate is effected.

In testimony whereof I affix my signature, in presence of twowitnesses.

SAM EVERETT FINLEY.

Witnesses:

I M. L. BELLAMY, C. B. HARMAN'. 

